bug#22324: 25.0.50; completion-category-defaults style doesn't override completion-styles (gets prepended instead)

[Dmitry Gutov <dgutov@yandex.ru>]

On 02.12.2021 12:10, Lars Ingebrigtsen wrote:
> ---
> This overrides the defaults specified in `completion-category-defaults'."
> ---
> 
> And it does indeed prepend:
> 
> (defun completion--category-override (category tag)
>    (or (assq tag (cdr (assq category completion-category-overrides)))
>        (assq tag (cdr (assq category completion-category-defaults)))))
> 
> But...  I think saying that that "overrides" is fine?

I think an "override" has a particular meaning, and that's replacing 
something that was there before. Not prepending to it.

Why is it important? Suppose the "category defaults" entry has a 
"permissive" style set up for a certain completion category.

As a user, I might try to override it with an entry in 
completion-category-overrides, to use a stricter style like 
'partial-completion' or even 'basic'.

But what happens when my input fails to find any completions with the 
style I specified? It will fall back the default one, which is both 
surprising, given the current documentation, and can be problematic with 
respect to performance ('flex' is slower than 'partial-completion') and 
behavior (bringing lots of probably irrelevant completions which match 
my input because 'flex' is quite lax).

Whether one enjoys the lax behavior of 'flex', is more or less a user 
preference, and it seems one can't configure it entirely through 
completion-category-overrides. And since that variable is a defcustom 
and completion-category-defaults is not, it seems like we're limiting 
customization this way.

Though, of course, a user that's motivated enough can change the value 
of completion-category-defaults too.